One unwelcome visitor to my garden at this time of year is powdery mildew. Here’s how to control this plant disease with natural remedies, including a homemade baking soda spray treatment.
Signs of Powdery Mildew
It starts as white patches on the leaves of squash, lilacs, phlox, bee balm, and other plants, making them look like they have been dusted with baby powder. Early on, it wipes off or washes away only to return again.
Eventually, the affected leaves turn yellow and die on many plants while others continue to soldier on.
So far this year, only our squash have been affected.
Thankfully, there is no sign of it on other susceptible plants such as phlox.
Causes of Powdery Mildew
The lack of powdery mildew on my phlox is probably due to the fact that it is not caused by just one fungus, but by several different species that are attracted to different kinds of plants. The powdery mildew that you find on your squash is not the same as the mildew on your beans or roses. Cucurbits such as pumpkins, squash, cukes, and melons have three different powdery mildew fungi gunning for them that can thrive in both humid and dry weather. The spores of the fungi are windborne and can’t be avoided. No wonder the squash get hit every year!
Remedies for Powdery Mildew
There are lots of home remedies, but researchers have found that simply spraying with plain water weekly can be effective. The spores like humidity but hate rain and water. They can’t germinate or grow if the leaves are wet. This is the opposite of what most gardeners think, me included.
One season I tried to defeat powdery mildew by planting squash in our high tunnel, thinking that if I could keep the leaves dry they would not be affected. Naturally, they got the worst case of powdery mildew I have ever seen! It was the perfect place for it to thrive: high humidity and no rain hitting the leaves. Another lesson learned the hard way!
If you decide to try a home remedy rather than plain water, there are several that have been proven to be effective if used early. They can slow or stop the spread early on, but once the fungi are established in the leaves, they won’t eliminate it.
Homemade Baking Soda Spray
Many of these remedies include baking soda. Just be aware that baking soda can burn plants and it can build up in your soil, potentially causing deficiencies in calcium, magnesium, and iron. Potassium bicarbonate can be substituted for baking soda. Test these sprays on a small area first to make sure they do not damage your plants.
- Mix 1 tablespoon baking soda with 1 tablespoon vegetable oil and 1 teaspoon dish soap in 1 gallon of water.
- Mix 4 tablespoons baking soda with 2 tablespoons of Murphy’s oil soap in 1 gallon of water.
- Mix 2 to 3 tablespoons vinegar with 1 gallon of water. Be sure to test this first because vinegar can burn plants.
- Neem is an organic fungicide. Follow instructions on the label.
- Mix 1 part milk with 10 parts water.
- Some folks swear by mouthwash as an effective fungicide but it is not organic. They recommend 1 cup mouthwash to 3 cups of water.
To keep the fungi from developing a resistance to your homemade spray, it is recommended that you alternate remedies each week. Use baking soda one week and milk the next. Whether spraying with water or a home remedy, do it early in the day so the leaves can have a chance to dry before evening.
When adding new plants to your flower beds, look for mildew resistant varieties. Don’t over-fertilize with high nitrogen fertilizers since soft new growth is very susceptible to infection. Space plants far enough apart to promote good air circulation. If infection starts in lower leaves, snip them off. Make sure plants get enough direct sunlight. Prevention is the best medicine!
See more about Powdery Mildew Control.
Reader Comments
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Podwery Mildew on cucumbers, July 22, 2021-follow up
I researched and learned that a cucumber vine life-span is 70-80-days. My cucumber vine did die; however, it was past 70-days, had produced many cucumbers and I feel it died from age and not from the spray.
Podwery Mildew on cucumbers
Not sure about using baking soda. I had a beautiful cucumber that produced a colander of cucumbers each week. It began to get powdery mildew. I used the recipe according to instructions; sprayed early in the morning. The days afterward were cloudy and the vine looked healthy. Two weeks later, however, the vine is turning yellow; appears to be dying and there are no cuke. I have kept up the watering. I will begin watering with 20-20-20; maybe the baking soda leached out important nutrients...Not sure what happened?
Powdery Mildew
I started using Bee Safe 3-in-1 Garden Spray (Organocide) on my squash plants when I saw powdery mildew. The white spots faded within a day and I simply spray every few days as more appears (which is not very much). This product contains sesame oil so may be available in other forms as well.
Rust spots on plants
I’m not sure of the most effective way to get rid of this. There are also repeated holes. I did find micro black and pale yellow dots on the undersides. Help needed re rust and yellow leaves on my cake leaves and okra. Thanks
Powdery Mildew on Peonies
Every year my peony bushes get powdery mildew really bad. Is the water/other additives you recommend spraying good for peonies??
Spraying the leaves now won’t
Spraying the leaves now won’t hurt them but it won’t help either. To really do any good you should start spraying the new growth in the spring before the mildew starts as a preventative. If the leaves are terribly afflicted, cut them off and be sure to remove any other leaves that fall at the end of the season to get rid of fungal spores that will infect the plant next year.
Powdery Mildew on Peonies Easy Help
The previous response here to your question, along with info I also found here at Farmer's Almanac, helped me tremendously to (mostly) vanquish the powdery mildew on my peonies. I was surprised to learn that washing down the plants would help. It seems counter intuitive to use water to combat mildew, but it really works! Last season, the lovely foliage on my peonies looked awful, ravaged by mildew. This year, as soon as I noticed the mildew returning, I used a neem oil and water mix spray, coating all the leaves about twice a week. Do this at night. Alternate days that follow nights when you have not used the neem, spray down the plants in the morning so they can sun dry fully later in the afternoon. I use just a gentle shower from a rain spray attachment, no need to get out the pressure washer! Now, at the near end of the season, almost no mildew visible at all, glossy leaves, lovely green. If you notice a leaf cluster getting mildew, remove it. So a fast couple minutes about four times weekly with your peonies will eliminate the mildew. I'm extremely pleased with the advice I got here and the addition of the neem oil spray really seems to make a difference, too. (Bonus: a potted maple sapling that was getting maple fungus has been cured with the neem oil, too!)
Can you eat Tomatoes with powdery mildew?
Some of my tomatoes have powdery mildew on them, can I wash it off and eat them? What if I make sure to cook them, would that kill everything?
Thanks!
They might not taste as good
They might not taste as good as fruit from a plant that is not afflicted but powdery mildew will not hurt you.
Mildew on roses
Need the best solution to get rid of the mildew on my roses. Any suggestions?
Rose mildew is tough to deal
Rose mildew is tough to deal with. Use a fungicidal spray or try a homemade one of potassium bicarbonate mixed with just water. Prune out the worst parts. Make sure the plants are growing in full sun and in a location with good air circulation. Water deeply during dry spells. Clean up debris in the fall since the spores can overwinter. If all this fails and you still want to grow roses (I have given up) replace them with resistant varieties. Still no guarantees that they won’t get mildew too but they are less susceptible.
Repellent for Yellow Jacket
I cannot do garden work because of the yellow jackets flying and darting around me in a 'threatening manner' whenever I go within a range of 10 feet of their nest. How can I get rid of them.
Almost as simple as water
This year, I discovered that a simple solution of baking soda in water is effective enough to mitigate powdery mildew growth on zucchini, butternut squash and pie pumpkin leaves. 1 Tbsp in 1 Gal of water, applied twice a week with my little hand-pump sprayer, seems to be doing the trick without any adverse effect on the plants so far.